Grinding element



Sept. 26, 1944. E.'A. Kol-:THER

GRINDING ELEMENT Filedmg. 2s, 19213 'LQ-QM.

nfl llln.

Gftorncgs Patented Sept. 26, 19.44

Y Emil A. Koether, Baltimore, Md.

Original applicationy January 24, 1940, Serial No. 315,438. Divided andthis application August 23, 1943, Serial No. 499,687

1 Claim.

This invention relates to abradi'ng and particularly to means forimproving the accuracyof grinding operations by cooling the grindingelements as uniformly and as effectively as practicable and bysubstantially preventing the transfer of heat from the grinding memberto the supporting portions of the grinding machine, particularly theshaft bearings.

Arrest of the flow of heat from the grinding member to such supportingportions is a .sub-

stantial factor in the attainment of the desiredv result. Contrary towhat might be expected, tests show that arrest of this heat flow(Without stimulation of air cooling, and even when the grinding surfaceof the disc and the air iiow over this surface of the disc are thesame'as With conventional mounts) results in enhanced heat dissipation,as evidenced by marked reduction in the temperature of the dischargingground arti,-

cles. It is not here intimated that active cooling will not stillfurther improve the operating conditions, particularly` with heavy cuts.The significant fact is that arrest of heat flow from Athe grinding disctoits support has a benecial effect which is always substantial andunder some ing disc is unevenly heated, its form is affected andinaccuracies' result. Similarly, if the face plate on which the disc ismounted' is heated, and particularly if it is unevenly heated, similardistortions are caused. Finally, transmission of heat to the bearingsincreases the lubrication problem and requires the bearings to be morefreely fitted when cold than would be required if it could be 'assuredthat the bearings would run cool at all times.

The present invention involves the mounting of the grinding disc on theface plate in such a Way that the grinding disc is spaced uniformly fromthe face plate, is cooled approximately uniformly on its back face andonits grinding face,

and, hence, is conditioned to operate with the utmost precision so faras any distortion of the grinding disc itself is concerned. At thispoint it may be; mentioned that a resin bonded Wheel is believed totransmit heat better than a ceramic wheel, so that the problem of unevenheating is lessy acute with the former than the latter. A

conditions appears to be as important as stimulated air cooling. Botheffects are` present in the Vpreferred embodiments of the invention.

While the invention may be adapted to grind- Vers of various types, itnds itsgreatest utility in v connection with face grinders in which an`abrasive disc is mounted on a face plate and the kgrinding `is carriedout on the plane surface of the grinding disc. Grinders of this typegener'- ate heat quite rapidly, and thisis particularly true of facegrinders in Which two opposed discs Yafford a xe'd gap through which thearticlesto be lground are fed in a substantially continuous stream. Atypical example of such grinders is the type used for grinding the planefaces of piston tov this particular class of machine with markedsuccess. l

In the prior art, cooling during grinding has been provided for but ithasbeen directed prias practicable' Athroughout the: grindingjdisc.'

The efects of heat are numerous andl diverse, a'ndaffectthegrinding'operation to anlvextent ,that was not appreciated until'atenuar@` cooling jvvas'ha'd.' Heating'affects'accurac'y; If the grind-A ring blanks and the invention has been applied A 45 marily to4safeguarding the article being ground fafgainst, undue heating. 'Very'little consideration ,has been given in the past to cooling oftheY`grindingelements themselves, or to the ideaof maintaining uniformityof temperature as' nearly Bakelite resin bonded Wheel has a coefficientof expansionwhich approximates that of cast-iron,

-a point which is not Without signicance in view of the mode of mounting,the discs. Further, the face plate is similarly cooled, and thustheheat `is dissipated at or near its source and is not transmitted tothe face plate in any considerable degree. l y

As a consequencefonly a negligible portion of the heat developed by thegrinding operation is transmitted through the shaft to the bearings,with the result that the bearings always run un- Vder normal temperatureconditions and can be fitted Withthe utmost precision practicable in thebearing art, without risk that they will ever run hot.

'All' of these factors contribute to accuracy of grinding, but they haveanother and unexpected secondary result. The rate of development of heatincreases rapidly as the abrasive becomes finer, and the heat effectsimpose a practicable limit on the iineness of the abrasive used incommercial grinding operations in which a substantial production rate isto be maintained. The

Yeffective and uniform cooling characteristic of Athe present inventionpermits the use of much ner abrasive at commercial rates and actuallypermits the production by grinding operations of Hfinishes notheretofcrecommercially produced ex- 'cept bythe coarser lapping operations. Sincethe production rate of a'grinder is manytimesfthat of a lapping machine,lthe commercial importance `of this secondary result is marked.

The invention contemplates the support of the disc on the face plate insuch a way that the closest practicable approach to a continuous air gapbetween the disc and the plate is afforded. It contemplates further, theiiow of air between the proximate faces of the grinding discs where twoopposed discs are used and the iiow of air between each disc and itsface plate.

In referring to air as the cooling medium, its ready availability is acontrolling consideration and the possible use of other gases isappreciated.

As indicative of the importance of the invention, it may be said thatprecision is appreciably improved, the over-all life of a grinding discis increased by about one-iifth of its normal life as heretofore used,and the periods when the machine is out of operation for the purpose ofdressing the discs are reduced by about onethird of the number of suchperiods formerly required. Thus, productivity of the grinding machine issubstantially increased. The figures given are conservative andar-eexceeded in certain types of grinding operations.

The -possibility of using nner grits on the wheels has already beensuggested. This possibility arises from a reduced tendency to glaze.There is also 'less tendency of the'grinding disc to assume what theoperators call a smeary appearance. impairment of the grinding operationand while 4the exact cause is not known, it vhas been atsubject tovariations to meet requirements of particular cases. is much moreimportant, but it, too, is subject to some variation to conform tolimits imposed v by the nature of the grinding machine or to meetspecial requirements incident to the form or material of the piece to beground.

The preferred embodiment of the invention will now be described inconnection with the accompanying drawing, in which:

Figure 1 is a View of the'rear face of va grinding disc showing theconnecting bushings arranged according to a pattern known in theface-grinding art, but indicating the use of special connectionsaccording to the presentinvention;

Fig. 2 is an enlarged fragmentary section showing the connection betweenthe disc of Figure `1 and the face plate upon which it is mounted; and

Fig. 3 is an axial section through the grinding elements of a doubledisc grinder constructed according to the patent to Koether, No.2,169,252, dated August 15, 1939, and indicating one mode of applyingthe invention which has Ydemonstrated marked utility. In this view thesupporting bearings and driving motors are not indicated, the purposebeing to simplify the view by limiting it to those features which aredirectly involved in the cooling function.

The path of flow of the air This appearance is attended 'with f lair isinduced is a secondary consideration and -at its center and is providedat its rear face with a number of tapped inserts I3. These inserts areof a form better shown in Fig. 2 and receive bolts I4 which pass throughthe face plate I5 of ordinary form and connect the grinding disc to theface plate rigidly while maintaining between the proximate faces of theplate and disc, that is, between the forward face of the plate and therear face of the disc, an air gap which is substantially continuous. Theinserts I3, as indicated in Figure 2, are formed to include the spacingelements.

The arrangement described contemplates that the simple rotation of thegrinding disc and its face plate will induce active flow of air throughthe interval between the face plate and the disc and usually this airwill enter the central aperture l2 and ow outward. Practically allgrinding wheels are shrouded or enclosed and the shroud is provided`with an air suction Aconnection which, in the old type of grinder wasdesigned rchieiiy to carry away dust. According to the presentinvention, this offtake assumes al. new and secondary function ofstimulating cooling air flow, and for best results it is considereddesirable to increase the suction beyond that customarily usedheretofore, thus circulating a greater quantity of air, to secure anadequate cooling eifect.

Face grinding machines using a single grinding disc are known, but amore desirable form involves the use of two grinding discs. One formusing `two opposed discs, shown in the patent to Morton, No. 1,640,715,dated August '30, 1927, has the axes of the discs offset. The presentinvention can be used in such grinders. However, the offset disc type ofgrinder is being supplantedby the double disc type of grinder shown inthe patent to Koether, above identified,

Ain which there are two pairs of coaxial discs opposed to each other..The inner and outer discs of a given pair have their grinding faces inthe same plane, and they are driven -at different speeds', and quitecommonly in `opposite directions. These details depend on the type ofnish desired.

The purpose of subdividing one vgrinding unit linto two concentric parts-driven at different angular velocities is to secure higher linealspeeds in the Acentral grinding area so that the disparitybetweengrinding speeds near the center and at the outer limits will not be toogreat.

4same plane and their aXes are concentric, so

that the inner grinding unit 2B turns concentrically within'theouterunit 25. Each of the .grinding elements is connected to its face plateby rigid spacing connections generally indicated by the vreferencenumeral 2], and illustrated as conforming to the showing in Figure 2.

. A pair of trackways 28 and `29 extend between the discs andarenarrower than the interval 'between the grinding faces. 'These servevto guide aseries of'piston ring blanks, one of whichapand also throughthe slots which accommodate the guide tracks 28 and 29,

Grinding discs rotate at quite high speeds and there is a moderatecentrifugal impelling effect so that air is drawn in through the centralaperture of the inner grinding member and flows thence outward throughthe intervals between the various grinding members and their faceplates. The

effect is to keep the grinding members cool and at uniform temperature,front and back. As indicating the effectiveness of such cooling, it maybe said that a given grinder of the type illus- -trated in Figure 3operating according to the invention, is so effectively cooledthat'immediately after it is stopped, it is possible to place the handon the grinding surface even of the inner disc which is the one wherehighest temperatures always exi-st.

Prior to the application of the invention, so much heat was developedand transmitted through the shafts to the bearings that after themachine had been running for two hours or more, the bearing housingswere too hot to touch.

After the application of the invention, the bear-y ings were onlyslightly warm following many hours of running.

The inventive concept is not limited to any particular manner ofcirculating the air. It resides rather in the idea that the grindingdiscs are supported in such a way that a heat-insulating air gap isafforded between thev disc and. the

supporting face plate and some means is provided to cause or permitcirculatory ow of air. The effect is to dissipate the heat and maintainthe grinding discs at substantially uniform temperature throughout thegrinding operation.

The present application. is a division of my allowed application Ser.No. 315,438 filed January 24, 1940Which has issued as patent 2,329,995,Sept. 21, 1943 and is directed to the structure of a grinding disc whichhas demonstrated peculiar utility in the performance of the invention.

What is claimed is: A grinding component for that type of grindingmachine which has a power driven rotatable face plate on which ismounted coaxially a grinding disc with its grinding face parallel withthe face of said face plate, said grinding element comprising a disc ofsubstantial thicknes-s and composed of bonded abrasive material, saiddisc having its working face in a plane perpendicular to its axis ofrotation and having inset permanently in its back and distributed overits back surface in substantially symmetrical relation to its axis andperiphery a multiplicity of inserts, each insert having a shank whichprojects into the disc and is permanently xed therein, and a flat headseated on the back face of the disc, said inserts being provided withthreaded sockets normal to the back face of the disc and adapted toreceive threaded retaining means for rigidly attaching the disc toa faceplate with the outer faces of the heads of said inserts engaging theface plate, all of said inserts having the outside faces of their saidexpanded heads in a common plane, parallel with the plane of thegrinding face of the disc and spaced away from the rear face of suchdisc suiiiciently to afford an adequate interval between the back faceof the disc and the plane of the outer face of the heads of the inser-tsto permit the circulation of air in quantity sufficient to'maintain thetemperature of the disc when in operation. f

EMIL A. KOETI-IER.

